If input and stdin parameters are passed as keyword arguments to subprocess.run, an exception is thrown even if input and stdin are both None.

The exception is ValueError: stdin and input arguments may not both be used.

I attach a minimal working example of the bug

What is wrong with this?

subprocess.run('ls', input=b'', stdin=None) # this is ok

kwargs = {'input': b'', 'stdin': None}
subprocess.run('ls', **kwargs) # this throws exception

The two calls should have the same behaviour, but one throws exception and the other doesn't. I think the exception shouldn't be thrown, because stdin is None.

I just tried:

    subprocess.run('ls', input=b'', stdin=None)

and I got the same ValueError as for passing using kwargs. Where did you get the idea subprocess.run('ls', input=b'', stdin=None) worked?

The actual code receives input by name, but stdin is received in **kwargs. The test is just:

    if input is not None:
        if 'stdin' in kwargs:
            raise ValueError(...)
        kwargs['stdin'] = PIPE

Perhaps just change `if 'stdin' in kwargs:` to:

    if kwargs.get('stdin') is not None:

so it obeys the documented API (that says stdin defaults to None, and therefore passing stdin=None explicitly should be equivalent to not passing it at all)?

> and I got the same ValueError as for passing using kwargs. Where did you get the idea subprocess.run('ls', input=b'', stdin=None) worked?

Sorry, the example was wrong. Both calls have the same behaviour.

> so it obeys the documented API (that says stdin defaults to None, and therefore passing stdin=None explicitly should be equivalent to not passing it at all)?

The actual problem is this. The fix you propose works for me.

I opened a PR with @josh.r proposed change.

New changeset 8cc605acdda5aff250ab4c9b524a7560f90ca9f3 by Gregory P. Smith (Rémi Lapeyre) in branch 'master':
bpo-34886: Fix subprocess.run handling of exclusive arguments (GH-11727)
https://github.com/python/cpython/commit/8cc605acdda5aff250ab4c9b524a7560f90ca9f3

New changeset 6324ac1293b2cf71559869b88f89f510f9a62a8e by Miss Islington (bot) in branch '3.8':
bpo-34886: Fix subprocess.run handling of exclusive arguments (GH-11727)
https://github.com/python/cpython/commit/6324ac1293b2cf71559869b88f89f510f9a62a8e

New changeset 10b4fd98142edef6ab7b034e10ae5c9551043999 by Miss Islington (bot) in branch '3.7':
bpo-34886: Fix subprocess.run handling of exclusive arguments (GH-11727)
https://github.com/python/cpython/commit/10b4fd98142edef6ab7b034e10ae5c9551043999

thanks!